SAMPLED-DATA SIMULATION OF PERIODICALLY SWITCHED NONLINEAR CIRCUITS - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 145

There are many interpolation techniques available. Polynomial-based in-
terpolation, such as, Lagrange interpolation and Newton finite difference
interpolation [62], are effective for low-order interpolation and become
unstable once the order is high [63]. Exponential interpolation [64] is
effective only if the exponents are known. Fourier series interpolation is
an efficient interpolation method [63, 65]. The order of the interpola-
tion can be well above 1000 while still preserving the numerical stability.
An important advantage of high-order Fourier series interpolation is the
high accuracy of approximation.
To minimize the cost of computation, a simulation window of width
as shown in Fig.7.4, is employed. in the window is approxi-
mated using an interpolating Fourier series
where is given by [64, 66]